This application is based on application No. H11-372192 filed in Japan on Dec. 28, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical module employing a photonic crystal for multiplexing and demultiplexing optical signals, and to a method for manufacturing such a module.
2. Description of the Prior Art
In recent years, communications systems using optical fibers for connecting individual households to a communications center (hereinafter, such a system will be referred to as an FTTH (fiber to the home) system) have been becoming popular. An FTTH system requires optical network units equipped with an optical module for multiplexing and demultiplexing optical signals.
For example, to the optical network unit installed in each household is delivered, by way of a single optical fiber, down-link light carrying multichannel video signals and having a wavelength of 1.5 xcexcm and up- and down-link light carrying low-speed digital signals for two-way communication and having a wavelength of 1.3 xcexcm. The optical network unit performs demultiplexing to separate the delivered light into video signals having a wavelength of 1.5 xcexcm and down-link digital signals having a wavelength of 1.3 xcexcm, and performs also multiplexing to mix up-link digital signals from the household with the light so as to send them out.
Conventionally, as an optical module having functions as described above, an optical module employing an optical coupler, as shown in FIG. 1, is used. The optical signals entering it via a terminal 1 is demultiplexed by a filter 3 inserted in a waveguide 2 into light with a wavelength of 1.5 xcexcm and light with a wavelength of 1.3 xcexcm.
The light having a wavelength of 1.5 xcexcm is reflected by the filter 3 and exits via a terminal 4; on the other hand, the light having a wavelength of 1.3 xcexcm is transmitted therethrough and exits via a terminal 5. Another terminal 6 serves as an input terminal for the up-link digital signals having a wavelength of 1.3 xcexcm, and the up-link digital signals fed in via this terminal 6 pass through the filter 3 and travel backward so as to exit via the terminal 1.
An optical module as shown in FIG. 1 is manufactured as follows. First, a waveguide 2 having a desired shape is formed on a substrate 7. Then, by reactive-ion etching (hereinafter, referred to as RIE) or mechanical cutting, a slit 38 is so formed as to have a desired angle relative to the waveguide 2. A filter 3 is inserted in the slit 38 and fixed with adhesive.
The filter 3 is usually formed out of a dielectric multilayer film, and is ideally designed to exhibit 100% reflectance for light having wavelengths of 1.5 xcexcm or longer and 100% transmittance for light having wavelengths less than 1.5 xcexcm.
However, manufacturing an optical module having a structure as described above requires very delicate adjustment when a filter 3 is fitted thereto. This sometimes leads to lower reliability due to, for example, uneven accuracy. Furthermore, because the filter 3 and the waveguide 2 are produced in separate steps, coordination is needed between the progress of the two steps and a larger number of pieces of equipment are needed. This inconveniently leads to higher manufacturing costs.
An object of the present invention is to provide an optical module high in reliability and low in manufacturing costs, and to provide a method for manufacturing such an optical module.
To achieve the above object, according to one aspect of the present invention, an optical module is provided with: a substrate, a waveguide, formed on the substrate, for guiding light; and a photonic crystal portion that has media having different refractive indices arranged in a periodic pattern and that is disposed in a channel of the waveguide on the substrate, wherein the photonic crystal and the substrate are integrally formed.
According to another aspect of the present invention, a method for manufacturing an optical module is provided with: an aluminum film formation step for forming an aluminum film on a conductive substrate; a protective film formation step for forming a protective film on the aluminum film; an exposure step for exposing the aluminum film by removing the protective film within a predetermined area; an anodization step for forming a photonic crystal formed of a porous material by anodizing the aluminum film within the predetermined area; a removal step for making the photonic crystal project by removing the protective film and the aluminum film; a lower cladding formation step for forming a lower cladding layer on the substrate; a core formation step for forming a core layer on the lower cladding layer; a waveguide formation step for forming a waveguide by patterning the core layer into a predetermined shape; and an upper cladding formation step for forming an upper cladding layer covering the waveguide.